Recording/reproducing apparatus including an optical pickup having an objective lens compatible with a plurality of optical disk formats

ABSTRACT

A recording/reproducing apparatus including an optical pickup compatible with a plurality of optical recording media each using light of a different wavelength. The optical pickup includes at least one light source, an objective lens having a function of focusing light emitted from the light source into the optimal light spot on an information recording surface of one of the plurality of the optical recording media, and a light detector to detect light transmitted through the objective lens after being reflected from the information recording surface of the optical recording medium on which the light spot is formed. The objective lens has an inner area, an annular lens area and an outer area such that the annular lens area divides the inner area from the outer area and has a ring shape centered at a vertex. The inner area, the annular lens area and the outer area have aspherical surface shapes.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of application Ser. No.09/594,509, filed Jun. 16, 2000, now pending, which is acontinuation-in-part of application Ser. No. 09/023,046, filed Feb. 13,1998, which issued as U.S. Pat. No. 6,091,691, which claims the benefitof Korean Application No.4273/1997, filed Feb. 13, 1997, in the KoreanPatent Office, and U.S. Provisional Application No. 60/039,663, filedFeb. 28, 1997, the disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a recording/reproducingapparatus including an optical pickup having an objective lens with afunction of forming an optical spot on an information recording surfaceof optical recording media of different formats, and more particularly,to a recording/reproducing device including an optical pickup having anobjective lens which is compatibly used in a plurality of optical diskseach having a different format, such as a digital versatile disk (DVD),a CD-Recordable (CD-R), CD-Rewritable (CD-RW), a Compact Disc (CD) and aLaser Disk (LD).

[0004] 2. Description of the Related Art

[0005] A recording medium for recording and reproducing information suchas video, audio or data at high density, is a disk, a card or a tape.However, a disk-type recording medium is primarily used. Recently, anoptical disk system has been developed in the form of an LD, a CD and aDVD. However, when optical disks having respectively different formats,such as DVD, CD-R, CD, CD-RW and LD, are compatibly used, opticalaberration occurs due to the variation of disk thickness and wavelength.Thus, an optical pickup which is compatible with the different formatsof the disks as well as removes the above-mentioned optical aberrationhas been actively studied. In the result of such a study, opticalpickups which are compatible to the different formats have beenfabricated.

[0006]FIGS. 1A and 1B show a part of a conventional optical pickup whichis compatible with different formats. FIG. 1A shows a case where lightis focused on a thin optical disk and FIG. 1B is a case where light isfocused on a thick optical disk. In FIGS. 1A and 1B, a reference numeral1 denotes a hologram lens. 2 denotes a refractive objective lens, 3 adenotes a thin optical disk, and 3 b denotes a thick optical disk. Light4 output from an unshown light source is diffracted by a grating(lattice) pattern 11 of the hologram lens 1, to accordingly generatenon-diffracted zero-order light 40 and diffracted first-order light 41,respectively. The non-diffracted zero-order light 40 is focused on aninformation recording surface of an optical disk 3 a by the objectivelens 2. The diffracted first-order light 41 is focused on an informationrecording surface of an optical disk 3 b by the objective lens 2.Therefore, the optical pickup shown in FIGS. 1A and 1B uses thenon-diffracted zero-order light 40 and the diffracted first-order light41 to record information on or read the information from the opticaldisks 3 a and 3 b of the different thicknesses, respectively.

[0007] Another conventional technology is disclosed in Japanese PatentLaid-open Publication No. Heisei 7-302437, published on Nov. 14, 1995.An objective lens of an optical head apparatus disclosed in the abovepublication has, from the center of the objective lens, an odd-numberedregion(s) having a focal point congruent with an information recordingsurface of a thin optical disk, and an even-numbered region(s) having afocal point congruent with an information recording surface of a thickoptical disk. Thus, in the case of the thin optical disk, lighttransmitted through the odd-numbered region(s) of the objective lens isused to read information from the thin optical disk. Also, in the caseof the thick optical disk, light transmitted through the even-numberedregion(s) of the objective lens is used to read information from thethick optical disk.

[0008] However, since the optical pickup shown in FIGS. 1A and 1Bdivides the incident light into zero order light and first order light,the efficiency of a light use efficiency is lowered. That is, since theincident light is divided into zero order light and first order light bythe hologram lens 1, only the zero-order light or the first-order lightis used to record the information on or read the information from theoptical disk, and the optical pickup uses only 15% or so of the incidentlight, to thereby lower the light use efficiency. Also, according to thethickness of the used optical disk, only one of the zero-order light andthe first-order light reflected from the corresponding optical disk 3 aor 3 b contains actually read information. Thus, the light having noinformation functions as noise in a light detection operation withrespect to the light containing information. The above problem can beovercome by processing the hologram lens 1 of the lens device. However,when working the hologram lens 1, an etching process for producing afine hologram pattern requires a high precision. Thus, the manufacturingcost increases.

[0009] In the case of the prior art disclosed in the Japanese PatentLaid-open Publication No. Heisei 7-302437, the light transmitted throughonly one of the odd-numbered region(s) and the even-numbered region(s)is used. As a result, the light use efficiency is lowered. Also, sincethe number of the focal points is always two, the light having noinformation functions as noise during the light detection, which makesit difficult to detect information from the light reflected from theoptical disk.

SUMMARY OF THE INVENTION

[0010] To solve the above problem, it is an object of the presentinvention to provide an optical pickup which has an excellent signaldetection function independent of a disk format thereof.

[0011] It is another object of the present invention to provide anobjective lens which compatibly is used with at least two substrateshaving respectively different thicknesses.

[0012] Additional objects and advantages of the invention will be setforth in part in the description which follows and, in part, will beobvious from the description, or may be learned by practice of theinvention.

[0013] The above and other objects of the present invention are achievedby providing a recording/reproducing apparatus including an opticalpickup which is compatible with a plurality of optical recording media,the optical pickup including at least one light source, an objectivelens having a function of focusing light emitted from the light sourceinto an optimal light spot on an information recording surface of one ofthe plurality of the optical recording media, and a light detector todetect light transmitted through the objective lens after beingreflected from the information recording surface of the opticalrecording medium on which the light spot is focused. The objective lenshas an inner area, an annular lens area and an outer area which aredivided by an annular lens area in a ring form centered at a vertex,wherein the inner area, the annular lens area and the outer area haveaspherical surface shapes for focusing light transmitted through theinner area and the outer area into a single light spot by whichinformation can be read from the information recording surface of arelatively thin first optical recording medium and scattered lighttransmitted through the annular lens area located between the inner areaand the outer area cannot be focused on the first optical recordingmedium during reproduction of the first optical recording medium havinga thin substrate. The objective lens focuses light transmitted throughthe inner area and the annular lens area into a single light spot bywhich information can be read from the information recording surface ofa relatively thick second optical recording medium and scattered lighttransmitted through the outer area cannot be focused on the secondoptical recording medium having a thick substrate, during reproductionof the second optical recording medium.

[0014] The above and other objects may further be achieved by providinga recording/reproducing apparatus including an objective lens which usesat least two substrates having respectively different thicknesses to uselight, the objective lens including an inner area, an annular lens areaand an outer area which are divided by an annular lens area in a ringform centered at a vertex, wherein the inner area and the outer areahave aspherical surface shapes for focusing light transmitted throughthe inner area and the outer area into a single light spot by whichinformation can be read from the information recording surface of arelatively thin first substrate. The annular lens area has anotheraspherical surface shape for scattering light transmitted through theannular lens area and is located between the inner area and the outerarea so that the transmitted light cannot be focused on the firstsubstrate with the thinner thickness. The objective lens focuses lighttransmitted through the inner area and the annular lens area into asingle light spot by which information can be read from the informationrecording surface of a relatively thick second substrate and scatterslight transmitted through the outer area so that the transmitted lightcannot be focused on the second substrate with the thick thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] These and other objects and advantages of the invention willbecome apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

[0016]FIGS. 1A and 1B show a conventional optical pickup having ahologram lens and a refractive objective lens;

[0017]FIG. 2A shows that an objective lens according to first and secondembodiments of the present invention forms an optical spot on aninformation recording surface of a thin optical disk;

[0018]FIG. 2B shows that the objective lens according to the first andsecond embodiments of the present invention forms an optical spot on aninformation recording surface of a thick optical disk;

[0019]FIG. 2C shows an objective lens according to the first and secondembodiments of the present invention as viewed from a light source,which shows sections of an inner area, an annular lens area and an outerarea of the objective lens;

[0020]FIG. 2D shows an enlarged annular lens area portion of an idealannular lens of the present invention;

[0021]FIG. 3A shows longitudinal spherical aberration of the objectivelens according to the first embodiment of the present invention duringreadout of a thick optical medium;

[0022]FIG. 3B shows wavefront aberration of the objective lens accordingto the first embodiment of the present invention during readout of athick optical medium;

[0023]FIG. 4 shows an objective lens according to the first embodimentof the present invention;

[0024]FIG. 5 shows an enlarged annular lens portion of the objectivelens according to the second embodiment of the present invention;

[0025]FIG. 6 shows a first type optical system of an optical pickuphaving a single light source adopting an objective lens according to thefirst and second embodiments of the present invention;

[0026]FIG. 7 shows a modification of the optical system of the opticalpickup shown in FIG. 6;

[0027]FIG. 8A shows a second type of optical pickup having an objectivelens, two light sources and a single light detector according to thefirst and second embodiments of the present invention;

[0028]FIG. 8B shows a modification of the optical pickup shown in FIG.8A;

[0029]FIG. 9 shows a third type of optical pickup having an objectivelens, two light sources and two light detectors according to the firstand second embodiments of the present invention;

[0030]FIG. 10 shows distribution of the light beams in the lightdetector when a thin optical disk is read by using the optical pickupaccording to the first and second embodiments of the present invention;and

[0031]FIG. 11 shows distribution of the light beams in the lightdetector when a thick optical disk is read by using the objective lensaccording to the first and second embodiments of the present invention.

[0032]FIG. 12 is a block diagram of a recording/reproducing apparatusfor implementing the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Reference will now made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tothe like elements throughout. The embodiments are described below inorder to explain the present invention by referring to the figures.

[0034]FIG. 2A through 2D show an objective lens according to the presentinvention. FIG. 2A shows optical paths when a working distance of theobjective lens 20 is “WD1” during readout of a thin optical disk 30A.FIG. 2B shows optical paths when a working distance of the objectivelens 20 is “WD2” during readout of a thick optical disk 30B. FIG. 2Cshows an objective lens 20 viewed from a light source, which shows thata lens surface 22 lying in the light source side of the objective lens20 is divided into an inner area (central region) A1, an annular lensarea (intermediate region) A2 and an outer area (periphery region) A3.FIG. 2D is an enlarged view of the portion of the annular lens area A2of the objective lens 20, where the objective lens 20 is ideallymanufactured.

[0035] In the objective lens 20 according to the first embodiment of thepresent invention, the lens surface 22 which lies in the light sourceside of the objective lens 20 is divided into the inner area A1, theannular lens area A2 and the outer area A3, by the annular lens area A2having a ring form such as an elliptical or circular shape with a vertexV1 of the lens surface 22 in the center. Here, the vertex V1 is a pointwhere the axis of the objective lens 20 intersects the lens surface 22of the light source side. The inner area A1 and the outer area A3 haveaspherical surface shapes which are optimized to form a best focal pointon the information recording surface 31A of the thin optical disk 30A.Also, the inner area A1 is fabricated to generate a little sphericalaberration on the information recording surface 31B of the thick opticaldisk 30B, but to have a sufficiently small spherical aberration forreadout of the thick optical disk 30B. Particularly, the inner area A1has a numerical aperture NA meeting the following relationship 1 toprovide an optimized optical spot for reproducing the thick optical disk30B such as an existing CD. The inner area A1, annular lens area A2, andouter area A3 respectively correspond to a near axis region, anintermediate axis region and a far axis region of incident light.

[0036] When light of 650 nm wavelength is used, it is preferable thatthe numerical aperture NA of the objective lens 20 is 0.37 or more toreproduce the existing CD.

0.8λ/NA˜spot size  . . . (1)

[0037] Here, λ represents the wavelength of the light, and NA representsthe numerical aperture of the inner area A1. Assuming that a workingdistance of the objective lens 20 is “WD1” where the best focal point isformed by the inner area A1 and the outer area A3, the light (rays)transmitted through the inner area A1 and the outer area A3 form theoptimal spot on the information recording surface 31A of the thinoptical disk 30A with respect to the working distance “WD1” and do notgenerate spherical aberration. Also, when the light transmitted throughthe inner area A1 of the objective lens 20 is used, the existing opticaldisk 30B such as a relatively thick CD is reproduced. This technologyhas been disclosed in Korean patent application No.96-3605. However, anumerical aperture not less than 0.4 is required to reproduce an opticaldisk which uses a smaller sized spot such as an LD among the existingoptical disks. To make large NA above 0.37, when the annular lens areaA2 has an aspherical surface extending the aspherical surface shape ofthe inner area A1, the light transmitted through the annular lens areaA2 during reproduction of the LD generates a larger optical aberrationto such a degree that the LD cannot be reproduced. Therefore, theannular lens area A2 corrects such optical aberration, and has anaspherical surface shape by which the light transmitted through theannular lens area A2 corrects the optical aberration at a best positionwhere a focal point is formed by the inner area A1.

[0038]FIG. 2B shows an optical path during reproduction of the thickoptical disk 30B, and shows that the light transmitted through the outerarea A3 does not form a spot on the optical disk and is scattered andthe light transmitted through the areas A1 and A2 are focused on thethick disk surface 31B. Meanwhile, when the working distance of theobjective lens 20 is “WD1,” the light transmitted through the annularlens area A2 is scattered at the information recording surface 31A ofthe optical disk 30A. The solid lines in FIG. 2A show the optical pathsof the light transmitted through the inner area A1 and the outer area A3when the working distance is “WD1.” The dotted line shows the opticalpath of the light transmitted through the annular lens area A2 in whichthe light is scattered.

[0039]FIG. 3A is a graph showing aberration for explaining a workingdistance and optical longitudinal spherical aberration of the objectivelens 20 during readout of a thick optical disk 30B. Since the inner areaA1 has spherical aberration when the objective lens 20 reproduces thethick optical disk 30B, the objective lens 20 is optically defocused,that is, the working distance is adjusted, to thereby have a minimalvalue of the optical aberration. A spherical aberration coefficient W₄₀produced due to the difference of a disk thickness between the thinoptical disk 30A and the thick optical disk 30B meets the followingequation 2. $\begin{matrix}{W_{40} = {\frac{n^{2} - 1}{8n_{3}}{d({NA})}^{4}\_ 0.6\quad {µm}}} & (2)\end{matrix}$

[0040] Generally, the optical aberration including spherical aberrationis expressed as the following equation (3).

W=W₂₀h²+W₄₀h⁴  . . . (3)

[0041] Here, W20 is a defocus coefficient and h is a marginal (light)ray height.

[0042] The square root of the optical aberration meets the followingequation 4. $\begin{matrix}{{\sigma_{W}^{2} = {\sqrt{\overset{\_}{W^{2}} - \left( \overset{\_}{W} \right)^{2}} = {{\frac{1}{12}\left\lbrack {W_{20} + W_{40}} \right\rbrack}^{2} + {\frac{1}{180}W_{40}^{2}\quad {Here}}}}},{\overset{\_}{W^{2}} = {{\frac{1}{3}W_{20}^{2}} + {\frac{1}{2}W_{20}W_{40}} + {\frac{1}{5}W_{40}^{2}}}},{\overset{\_}{W} = {{\frac{1}{2}W_{20}} + {\frac{1}{3}W_{40}}}}} & (4)\end{matrix}$

[0043] Therefore, the condition of the defocus coefficient whichminimizes the optical aberration is W₂₀=−W₄₀, and the actual defocusamount complies with the following equation (5). $\begin{matrix}{{\Delta \quad Z} = {{- \frac{2W_{40}}{({NA})^{2 -}}} - {8.3\quad {µm}}}} & (5)\end{matrix}$

[0044] Here, the variation of the numerical aperture (NA) of the innerarea, the disk refractive index (n) and the disk thickness (d) are asfollows: NA=0.38, n=1.58 and d=0.6 mm. If the annular lens area A2 isdesigned so that a best spot is formed and spherical aberration does notoccur with respect to the thick optical disk 30B being defocused by 8.3μm, the longitudinal spherical aberration graph as shown in FIG. 3A canbe obtained. In this case, the difference between a focal length formedby the inner area A1 and a focal length formed by the annular lens areaA2 becomes 8.3 μm owing to the defocus amount of 8.3 μm at the opticalaxis. And the focal length is 3.3025 mm for the inner area A1 and 3.3111mm for the annular lens area A2 according to the calculation by acommercial program (s/w) for optics. The 8.3 μm is a result from a thirdorder calculation by hand, but 8.6 μm is a result from a high ordercalculation including the third order by using the optical (s/w)program.

[0045] If the working distance of the objective lens 20 is changed from“WD1” to “WD2” which makes the optical aberration by the lighttransmitted through the annular lens area A2 into substantially zero,the light transmitted through the annular lens area A2 forms the opticalpath shown as the solid lines in FIG. 2B, and forms the optimal spot onthe information recording surface 31B of the thick optical disk 30B.When the working distance “WD2” is the optimal working distance forreproduction of the thick optical disk 30B, the annular lens area A2increases efficiency of utilization of the light used and increases thenumerical aperture as well. In this case, the inner area A1 maintainsspherical aberration which is sufficiently small for reproduction of thethick optical disk 30B. The spherical aberration generated by the innerarea A1 is minimized and total wavefront aberration is about 0.07 λms.Thus, the light transmitted through the inner area A1 and the annularlens area A2 forms a spot having a reduced size of 15% or more withoutincreasing the optical aberration on the information recording surface31B of the thick optical disk 30B, as compared with a case when theannular lens area A2 has the same aspherical surface shape as that ofthe inner area A1. Thus, it is possible to reproduce an opticalrecording medium such as an existing LD requiring a high density, aswell as a CD. In this case, the light transmitted through the outer areaA3 is scattered and does not influence the optical spot formed on theinformation recording medium 31B of the thick optical disk 30B. Theoptical path of the light transmitted through the outer area A3 is shownas the dotted lines in FIG. 2B. Thus, a single optical spot can beformed on the information recording surface 31B. Examples of the workingdistances described above and shown in FIGS. 2A and 2B are WD1=1.897 mmand WD2=1.525 mm.

[0046] When the recorded information is read, the thin optical disk 30Auses the light of the relatively short wavelength, while the thickoptical disk 30B uses both the light of the short wavelength and therelatively long wavelength. Therefore, when the thin optical disk 30A isa DVD and the thick optical disk 30B is a CD, an LD, CD RW or a CD-R,the inner area A1 and the outer area A3 have the aspherical surfaceshapes optimized to the information recording surface of the DVD, andthe inner area A1 and the annular lens area A2 have the asphericalsurface shapes where aberration is corrected and the working distance isoptimized so that the information can be reproduced with respect to theinformation recording surface of the CD, the LD, CD RW or the CD-R. Theannular lens area A2 among the areas A1, A2 and A3 has an asphericalsurface shape determined by the following equation (6) expressing theaspherical surface. $\begin{matrix}{{Z(h)} = {\frac{h^{2}/R}{1 + \sqrt{1 - {\left( {1 + K} \right){h^{2}/R^{2}}}}} + {A\quad h^{4}} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + Z_{offset}}} & 6\end{matrix}$

[0047] In the above equation (6), a function “Z” is a distance from thesurface perpendicular to the optical axis and passing through the vertexV1 of the objective lens 20 to the lens surface 22 lying on the lightsource side of the objective lens 20. A variable “h” is a distance fromthe axis of the objective lens 20 to a particular point perpendicular tothe axis. A constant “R” is a curvature which becomes a reference todetermine an aspherical surface shape. Z_(offset) is a parameter whichis newly introduced to express a step difference between the annularlens area A2 and the inner area A1. Since the equation (6) is well knownto a person who has an ordinary skill in the art, a detailed descriptionthereof will be omitted. The annular lens area A2 has a protruded shapeor a recessed shape when compared with the inner area A1 and the outerarea A3. The annular lens area A2 of the protruded shape is enlarged andshown in FIG. 2D. The aspherical surface shapes possessed by the innerarea A1 and the outer area A3 can be expressed by removing the offsetcomponent Z_(offset) in the equation (6). The width of the annular lensarea A2 is determined to provide the spot optimized for reproducing therelatively thick optical disk, and occupies at least 10% of an incidentsurface 22 of the objective lens 20 to which the light is incident fromthe light source. In case of a quantitative expression, the width of theannular lens area A2 has a range between about 100 and 300 μm.

[0048] The data obtained to provide the optimal aspherical surfaceshapes to the areas A1, A2 and A3 is represented in the following table.TABLE ASPHERICAL REFRAC- LENS CUR- SURFACE THICK- TIVE SURFACE VATURECOEFFICIENT NESS INDEX INNER AREA    2.13482 K: −0.425667 1.795 1.5864(A1)/OUTER A: −0.822095E-03 AREA (A3) B: −0.249645E-03 C: −0.106803E-03D: −0.194864E-03 Zoffset:   0.0 ANNULAR    2.14101 K: −0.425667 1.7951.5864 LENS AREA A: −0.362745E-03 (A2) B: −0.259541E-03 C: −0.665620E-03D: −0.620804E-03 Zoffset: −0.0012 LENS K:   8.578602 SURFACE (24) A:  0.897734E-02 TOWARD −14.39337 B: −0.341346E-02 OPTICAL DISK C:−0.762226E-03 D: −0.665163E-04 OPTICAL DISK    0 1.2/0.6 1.58

[0049] When the aspherical surface shapes of the areas A1, A2 and A3 aredetermined by the equation (6) and the above Table, the imaginarysurface which extends from the aspherical surface of the annular lensarea A2 expressed as the dotted line in FIG. 4 becomes farther than theaspherical surface of the inner area A1 from the vertex V1 of theobjective lens 20.

[0050] However, to easily form the areas A1, A2 and A3 of the asphericalsurface shapes on the lens surface lying on the light source side, it ispreferable that the annular lens area A2 is worked after working theinner area A1 and the outer area A3 primarily. Thus, the ring-shapedannular lens area A2 has a step difference at a region of contact withthe inner area A1 contacts or the outer area A3.

[0051]FIG. 4 shows an objective lens 20 which is worked so that a stepdifference exists in a region where the inner area A1 contacts theannular lens area A2. FIG. 5 shows an objective lens 20′ which is workedso that a step difference exists in a region where the annular lens areaA2 contacts the outer area A3. Such step differences generate aberrationdue to a light path difference between the light passing through theinner area A1 and the annular lens area A2. The step differences have aheight by which optical aberration due to the light path differencebetween the light passing through the inner area A1 and the annular lensarea A2 can be removed with respect to the light of a relatively longwavelength emitted from the light source or the light for reproductionof the thick optical disk. Particularly, the height of the stepdifference is determined so that a light path difference between thelight transmitted through the annular lens area A2 and the lighttransmitted through the inner area A1 of the objective lens 20 becomesan integer multiple of the wavelength of the used light as shown in FIG.3B. The step difference height is determined to be a value by which theoptical aberration due to the light path difference can be removed bytaking the offset Z_(offset) in the equation (6) and the width of theannular lens area A2 into consideration. Preferably, the step differenceheight is below 1.5 μm according to the refractive index of theobjective lens.

[0052]FIG. 6 shows a first type of optical pickup having a single lightsource adopting an objective lens 20 or 20′ according to the first andsecond embodiments of the present invention. The optical pickup shown inFIG. 6 has a typical optical system, which is compatible with opticaldisks of various different formats using the identical wavelength oflight, by using the objective lens 20 or 20′ according to the first andsecond embodiments of the present invention. The optical source 41 emitsthe laser beam of a particular wavelength. A light detector 43 isdesigned so that the light transmitted through the outer area A3 of theobjective lens 20 or 20′ is not detected during reproduction of thethick optical disk 30B. That is, the light detector 43 is designed sothat only the light transmitted through the inner area A1 and theannular lens area A2 of the objective lens 20 or 20′ is detected duringreproduction of information from the thick optical disk 30B.

[0053] For clarity, a case where the optical pickup of FIG. 6 includesthe objective lens 20 or 20′ and the optical source 41 emits the lightof 650 nm wavelength will be described. The (light) rays of 650 nmwavelength emitted from the light source 41 are reflected from a beamsplitter 42. The beam splitter 42 reflects about 50% of the incidentlight and the reflected rays become substantially parallel by acollimating lens 70. Since the (light) rays incident from the lightsource toward the objective lens 20 or 20′ can be made intosubstantially parallel light using the collimating lens 70, a morestable read operation can be performed. When a reproduction operationwith respect to a thin disk 30A, for example, a DVD is performed, the(light) rays transmitted through the collimating lens 70 are focused inthe form of a beam spot on an information recording surface 31A of thethin disk 30A by the objective lens 20 or 20′. In this case, theobjective lens 20 or 20′ has a working distance “WD1” and is shown as asolid line in FIG. 6 at position A. Therefore, the rays of 650 nmwavelength form a light path shown as the solid line in FIG. 6. Thelight reflected from the information recording surface 31A of the thindisk 30A is transmitted through the objective lens 20 or 20′ and thecollimating lens 70, and then is incident on the beam splitter 42. Thebeam splitter 42 transmits about 50% of the incident light and thetransmitted light is focused into the light detector 43 by a lightdetection lens 44. Here, the light transmitted through the inner area A1and the outer area A3 of the objective lens 20 or 20′ forms a spot of aparticular size on the information recording surface 31A of the thindisk 30A, by which information can be read from the informationrecording surface 31A of the thin disk 30A. Meanwhile, the lighttransmitted through the annular lens area A2 of the objective lens 20 or20′ forms a band in a scattered form at a position deviated by about 5μm on the disk 31B from the position of the spot formed by the lighttransmitted through the inner area A1 and the outer area A3. Thus, thelight transmitted through the annular lens area A2 is not detected bythe light detector 43 and does not function as noise with respect to aneffective reproduction signal during reproduction of data from the thindisk 30A.

[0054] When a reproduction operation with respect to a thick disk 30B,for example, a CD or LD, is performed, the light transmitted through thecollimating lens 70 is focused in the form of a beam spot on aninformation recording surface 31B of the thick disk 30B by the objectivelens 20 or 20′ at position B. In this case, the objective lens 20 or 20′has a working distance “WD2” and is shown as a dotted line in FIG. 6.Therefore, the light forms an optical path shown as the dotted line inFIG. 6. Here, the light transmitted through the inner area A1 and theannular lens area A2 of the objective lens 20 or 20′ forms a spot of asize on the information recording surface 31B of the thick disk 30B, bywhich information can be read from the information recording surface 31Bof the thick disk 30B. Meanwhile, the light transmitted through theouter area A3 of the objective lens 20 or 20′ forms a spot having arelatively weak intensity and lying at a position deviated from theposition of the spot formed by the light transmitted through the innerarea A1 and the annular lens area A2. Thus, the light detector 43 canread information from the thick disk 30B using the light transmittedthrough the inner area A1 and the annular lens area A2 of the objectivelens 20 or 20′.

[0055] In more detail, the light transmitted through the inner area A1generates spherical aberration on the information recording surface 31Bof the thick disk 30B. However, the spherical aberration has asufficiently small amount to read the signal from the thick disk 30B andthe minimized optical aberration is maintained by defocusing the lightby the amount of the spherical aberration at the optical axis. The lenscurvature and an aspherical surface coefficient of the annular lens areaA2 are corrected for a non-aberration optical system at the state wherethe working distance is adjusted to about 10 μm, so that additionalspherical aberration is not generated. Accordingly, the numericalaperture increases without increasing the optical aberration and thesize of the spot is reduced. Thus, an existing optical disk such as anLD requiring a higher-density than a CD can be reproduced. Forreference, a spot size of about 1.2 μm is needed to reproduce the LD,and that of about 1.4 μm is needed to reproduce the CD. A spot size ofabout 0.9 μm is needed to reproduce the DVD. As a result, the presentinvention can reproduce the various optical disks such as DVD, LD andCD, using a simple optical pickup.

[0056]FIG. 10 shows a distribution of the light in the light detector 43when information from a thin disk 30A is reproduced according to firstand second embodiments of the present invention. In FIG. 10, darkportions are due to the light transmitted through the inner area A1 andthe outer area A3 of the objective lens 20 or 20′ and are detected as anefficient reproduction signal. However, bright portions between the darkportions represent that the light transmitted through the annular lensarea A2 of the objective lens 20 or 20′ is not detected in the lightdetector 43 and is not detected as an efficient reproduction signal.FIG. 11 shows distribution of the light beams in the light detector 43when information from a thick optical disk 30B is reproduced using theobjective lens 20 or 20′ according to the present invention. A notation“B1” shows a distribution of the light transmitted through the innerarea A1 in the light detector 43, “B2” shows a distribution of the lighttransmitted through the annular lens area A2, and “B3” shows adistribution of the light transmitted through the outer area A3. Thelight forming the B1 and B2 distributions as shown in FIG. 11 isdetected as an efficient signal in the light detector 43, and the lightforming the B3 distribution is not detected as an efficient reproductionsignal.

[0057]FIG. 7 shows a modification of the optical system of the opticalpickup shown in FIG. 6. In FIG. 7, a unit 40 includes a light source 41and a light detector 43 which are formed in a single module. Aholographic beam splitter 50 is a polarizing hologram with a highoptical efficiency, and obtains a high optical efficiency by using aquarter wave plate 60. It is preferable that a polarizing hologramshould be replaced by a general hologram in the case when the quarterwave plate 60 is not used. The (light) rays of 650 nm from the lightsource 41 are transmitted through the holographic beam splitter 50 andthe quarter wave plate 60, and then become parallel rays by thecollimating lens 70. The objective lens 20 or 20′ focuses the lightincident from the collimating lens 70 on the information recordingsurface 31A of the thin optical disk 30A or the information recordingsurface 31B of the thick optical disk 30B, in the form of an opticalspot. In the optical pickup shown in FIG. 7, since the objective lens 20or 20′ is the same as that in FIG. 6, a detailed description thereofwill be omitted. The light reflected from the information recordingsurface 31A or 31B is finally converged to be focused on the lightdetector 43 by the hologram beam splitter 50.

[0058]FIG. 8A shows an optical pickup having an objective lens 20 or20′, two light sources 41 and 45 and a single light detector 43according to the first and second embodiments of the present invention.The light source 41 emits a laser beam of 650 nm and the light source 45emits a laser beam of 780 nm. The 780 nm light source may be used for aCD, CD-RW, CD-R or LD disk, and the 650 nm light source may be used fora DVD, LD, CD or CD-RW disk. When the light source 41 is used, theemitted light rays form an optical path shown as a solid line in FIG.8A, in which case the objective lens 20 or 20′ is shown as a solid lineat position A. When the light source 45 is used, the emitted light raysform an optical path shown as a dotted line, in which case the objectivelens 20 or 20′ is shown as a dotted line at position B. The optical spotfocused on the thick optical disk 30B or the thin optical disk 30A bythe objective lens 20 or 20′ is the same as that shown in FIG. 6.

[0059] A beam splitter 46 is a color separable splitter, which transmitsthe light supplied from the light source 41 and reflects the lightsupplied from the light source 45. The light reflected from the beamsplitter 46 is incident on a polarizing beam splitter 47. The polarizingbeam splitter 47 has an optical characteristic which transmits orreflects linearly polarized beams, which operates with respect to thelight of 650 nm and 780 nm wavelengths. The polarizing beam splitter 47transmits the light incident from the beam splitter 46, and thetransmitted light becomes a circularly polarized beam by a quarter waveplate 60. The circularly polarized beam is focused on the informationrecording surface of the thin optical disk 30A or the thick optical disk30B by the objective lens 20 or 20′. The light reflected from theinformation recording surface passes through the objective lens 20 or20′ and the collimating lens 70 and then becomes linearly polarizedlight by the quarter wave plate 60. The linearly polarized light isreflected from the polarizing beam splitter 47 and the reflected lightis focused into the light detector 43 by the light detection lens 44.The polarizing beam splitter 47 is replaced by a beam splitter whichpartially transmits and reflects the incident light when the quarterwave plate 60 is not used.

[0060] An optical pickup having an objective lens, two light sources, asingle light detector, and a plate-type beam splitter 42, can be used asshown in FIG. 8B. FIG. 8B shows a modification of the optical pickupshown in FIG. 8A, by replacing a cube-type beam splitter with aplate-type beam splitter. In addition, the two light sources 41 and 45face in opposite directions relative to one another and the lightdetector faces at a 90° angle to the light sources 41 and 45. This is incontrast to the optical pickup shown in FIG. 8A, wherein the lightsources 41 and 45 face at right angles relative to each other and thatthe light detector 43 faces in an opposite direction to that of thelight source 45 and at a right angle to the light source 41.

[0061]FIG. 9 shows an optical pickup having an objective lens 20 or 20′,two light sources 41 and 45 and two light detectors 83 and 105 accordingto the first and second embodiments of the present invention. In FIG. 9,the light source 41 emits (light) rays having a wavelength of 650 nm,the light detector 83 corresponds to the light source 41, and the lightsource 41 and the light detector 83. Reference numerals 45 and 105 are alight source and a light detector, respectively, for 780nm wavelengthlight, and 110 is a beam splitter. Other optical elements are the sameas those shown in FIGS. 8A and 8B. Since the optical pickup system shownin FIG. 9 can be understood by a person skilled in the art based on thedescription provided regarding FIGS. 8A and 8B, a detailed descriptionthereof will be omitted.

[0062] Up to now, the objective lens according to the present inventionhas been described with reference to the optical pickup. However, it isapparent to one having an ordinary skill in the art that the objectivelens according to the present invention can be applied to a microscopeor an optical pickup estimating apparatus.

[0063]FIG. 12 is a block diagram of a recording/reproducing apparatusfor implementing the present invention. The function of therecording/reproducing apparatus for recording/reproducing AN(audio/video) data using a recordable and rewriteable disk is largelydivided into recording and reproduction.

[0064] During recording, an AV codec 170 compression-codes an externallyapplied AV signal according to a predetermined compression scheme andsupplies size information for the compressed data. A digital signalprocessor (DSP) 120 receives the compressed AN data supplied from the AVcodec 170, adds additional data for error correction code (ECC)processing thereto, and performs modulation using a predeterminedmodulation scheme. A radio frequency amplifier (RF AMP) 130 converts themodulated data from the DSP into a radio frequency (RF) signal. Then, anoptical pickup 140 records the RF signal supplied from the RF AMP 130 ona disk mounted on a turn table of the optical pickup 140. The opticalpickup 140 may be any of those shown in FIGS. 6 through 9. A servo 150receives information necessary for servo control from a systemcontroller 160 and stably performs a servo function for the mounteddisk.

[0065] During playback of information data stored on the disk, theoptical pickup 140 picks up the optical signal from the disk having theinformation data stored therein, and the information data is extractedfrom the optical signal. The RF AMP 130 converts the optical signal intoan RF signal, and extracts the servo signal for performing a servofunction, and modulated data. The DSP 120 demodulates the modulated datasupplied from the RF AMP 130 corresponding to the modulation scheme usedduring modulation, performs an ECC process to correct errors, andeliminates added data. The servo unit 150 receives information necessaryfor servo control from the RF AMP 130 and the system controller 160, andstably performs the servo function. The AV codec 170 decodes thecompressed AN data supplied from the DSP 120 to output an A/V signal.The system controller 160 controls the overall system for reproducingand recording the information data from and on the disk mounted on theturn table of the optical pickup 140.

[0066] As described above, the recording/reproducing apparatus includingthe optical pickup according to the present invention is compatible withdisks having various different formats irrespective of the thickness orrecording density of the disk, and an excellent reading signal can beobtained from the used disk. Also, the objective lens according to thepresent invention can be manufactured at low cost by using an injectionmolding. Particularly, when two or more wavelengths are used for opticaldisk compatibility, an optical pickup can be made using a singleobjective lens and a single light detector.

[0067] While only certain embodiments of the invention have beenspecifically described herein, it will be apparent that numerousmodifications may be made thereto without departing from the spirit andscope of the invention.

What is claimed is:
 1. A recording and/or reproducing apparatuscompatible to a plurality of optical recording media having differentthicknesses, the recording and/or reproducing device comprising: anoptical pickup comprising a light source to emit light, an objectivelens to focus the light emitted from the light source into a singlelight spot on an information recording surface of one of the pluralityof the optical recording media, and a light detector to detect lighttransmitted through the objective lens after being reflected from theinformation recording surface of the one optical recording medium onwhich the light spot is focused, wherein said objective lens has aninner area, an annular lens area and an outer area centered at a vertex,the annular lens area having a ring shape and dividing the inner areafrom the outer area; the inner area, the annular lens area and the outerarea have aspherical surface shapes so as to focus the light transmittedthrough the inner area and the outer area into the single light spot bywhich information is read from the information recording surface of theone optical recording medium and to scatter the light transmittedthrough the annular lens area formed between the inner area and theouter area so that the scattered light is not focused on the informationrecording surface of the one optical recording medium if the one opticalrecording medium is a first optical recording medium having a firstthickness, and so as to focus the light transmitted through the innerarea and the annular lens area into the single light spot by whichinformation is read from the information recording surface of the oneoptical recording medium and to scatter the light transmitted throughthe outer lens area so that the scattered light is not focused on theone optical recording medium if the one optical recording medium is asecond optical recording medium having a second thickness greater thanthe first thickness; and a processing unit to process an informationsignal to control the light emitted from said light source, and toprocess the detected light from said light source, further comprising atleast one additional light source, each of the light source and the atleast one additional light source emitting light of differentwavelengths.
 2. The recording and/or reproducing apparatus according toclaim 1, further comprising a beam splitter having a beam splittingcharacteristic with respect to each of the plurality of the beamsrespectively emitted from the light source and the at least oneadditional light source.
 3. A recording and/or reproducing apparatuscompatible to a plurality of optical recording media having differentthicknesses, the recording and/or reproducing device comprising: anoptical pickup comprising a light source to emit light, an objectivelens to focus the light emitted from the light source into a singlelight spot on an information recording surface of one of the pluralityof the optical recording media, and a light detector to detect lighttransmitted through the objective lens after being reflected from theinformation recording surface of the one optical recording medium onwhich the light spot is focused, wherein said objective lens has aninner area, an annular lens area and an outer area centered at a vertex,the annular lens area having a ring shape and dividing the inner areafrom the outer area; the inner area, the annular lens area and the outerarea have aspherical surface shapes so as to focus the light transmittedthrough the inner area and the outer area into the single light spot bywhich information is read from the information recording surface of theone optical recording medium and to scatter the light transmittedthrough the annular lens area formed between the inner area and theouter area so that the scattered light is not focused on the informationrecording surface of the one optical recording medium if the one opticalrecording medium is a first optical recording medium having a firstthickness, and so as to focus the light transmitted through the innerarea and the annular lens area into the single light spot by whichinformation is read from the information recording surface of the oneoptical recording medium and to scatter the light transmitted throughthe outer lens area so that the scattered light is not focused on theone optical recording medium if the one optical recording medium is asecond optical recording medium having a second thickness greater thanthe first thickness; and a processing unit to process an informationsignal to control the light emitted from said light source, and toprocess the detected light from said light source, further comprising atleast one additional light source, wherein said first optical recordingmedium is a digital versatile disk (DVD) and said second opticalrecording medium is one of a compact disk (CD), a compact diskrecordable (CD-R), CD-Rewritable (CD-RW) and a laser disk (LD), when afirst one of the light sources emitting the light has a wavelength whichis adapted for the digital versatile disk (DVD) and a second one of thelight sources has a wavelength which is adapted for the compact diskrecordable (CD-R) are used.
 4. A recording and/or reproducing apparatuscompatible to a plurality of optical recording media having differentthicknesses, the recording and/or reproducing device comprising: anoptical pickup comprising a light source to emit light, an objectivelens to focus the light emitted from the light source into a singlelight spot on an information recording surface of one of the pluralityof the optical recording media, and a light detector to detect lighttransmitted through the objective lens after being reflected from theinformation recording surface of the one optical recording medium onwhich the light spot is focused, wherein said objective lens has aninner area, an annular lens area and an outer area centered at a vertex,the annular lens area having a ring shape and dividing the inner areafrom the outer area; the inner area, the annular lens area and the outerarea have aspherical surface shapes so as to focus the light transmittedthrough the inner area and the outer area into the single light spot bywhich information is read from the information recording surface of theone optical recording medium and to scatter the light transmittedthrough the annular lens area formed between the inner area and theouter area so that the scattered light is not focused on the informationrecording surface of the one optical recording medium if the one opticalrecording medium is a first optical recording medium having a firstthickness, and so as to focus the light transmitted through the innerarea and the annular lens area into the single light spot by whichinformation is read from the information recording surface of the oneoptical recording medium and to scatter the light transmitted throughthe outer lens area so that the scattered light is not focused on theone optical recording medium if the one optical recording medium is asecond optical recording medium having a second thickness greater thanthe first thickness; and a processing unit to process an informationsignal to control the light emitted from said light source, and toprocess the detected light from said light source, wherein the lightdetector is a single detector used to detect the light from said firstand second optical recording media as optical information, when at leasttwo of the plurality of light sources are used and said first and secondoptical recording media are compatibly reproduced.
 5. A recording and/orreproducing apparatus compatible to a plurality of optical recordingmedia having different thicknesses, the recording and/or reproducingdevice comprising: an optical pickup comprising a light source to emitlight, an objective lens to focus the light emitted from the lightsource into a single light spot on an information recording surface ofone of the plurality of the optical recording media, and a lightdetector to detect light transmitted through the objective lens afterbeing reflected from the information recording surface of the oneoptical recording medium on which the light spot is focused, whereinsaid objective lens has an inner area, an annular lens area and an outerarea centered at a vertex, the annular lens area having a ring shape anddividing the inner area from the outer area; the inner area, the annularlens area and the outer area have aspherical surface shapes so as tofocus the light transmitted through the inner area and the outer areainto the single light spot by which information is read from theinformation recording surface of the one optical recording medium and toscatter the light transmitted through the annular lens area formedbetween the inner area and the outer area so that the scattered light isnot focused on the information recording surface of the one opticalrecording medium if the one optical recording medium is a first opticalrecording medium having a first thickness, and so as to focus the lighttransmitted through the inner area and the annular lens area into thesingle light spot by which information is read from the informationrecording surface of the one optical recording medium and to scatter thelight transmitted through the outer lens area so that the scatteredlight is not focused on the one optical recording medium if the oneoptical recording medium is a second optical recording medium having asecond thickness greater than the first thickness; and a processing unitto process an information signal to control the light emitted from saidlight source, and to process the detected light from said light source,wherein said objective lens has a step difference which is formed in aregion where the annular lens area and the outer area contact each otherand makes a light path difference between the light transmitted throughthe inner area of said objective lens and the light transmitted throughthe annular lens area to have an integer multiple of a wavelength of thelight emitted from the light source, during reproduction of informationfrom the second optical recording medium.
 6. A recording and orreproducing apparatus compatible with at least two substrates havingrespectively different thicknesses and information recording surfaceswhich store information, the recording and/or reproducing devicecomprising: an objective lens comprising an inner area, an annular lensarea and an outer area centered at a vertex, the annular lens areahaving a ring shape and dividing the inner area from the outer area,wherein the inner area, the annular lens area and the outer area haveaspherical surface shapes so as to focus light transmitted through theinner area and the outer area into a single light spot by which theinformation is read from the information recording surface of a firstone of the at least two substrates which has a first thickness and toscatter the light transmitted through the annular lens area formedbetween the inner area and the outer area so that the scattered light isnot focused on the information recording surface of the first substrate,when the first substrate is to be used, and so as to focus the lighttransmitted through the inner area and the annular lens area into thesingle light spot by which the information is read from the informationrecording surface of a second one of the at least two substrates whichhas a second thickness greater than the first thickness and to scatterthe light transmitted through the outer lens area so that the scatteredlight is not focused on the information recording surface of the secondsubstrate, when the second substrate is to be used; and a processingunit which processes an information signal to control the lighttransmitted to the objective lens, and to process the light passedthrough the objective lens, wherein said objective lens has a stepdifference which is formed in a region where the annular lens area andthe outer area contact each other and the step difference makes a lightpath difference between the light transmitted through the inner area ofsaid objective lens and the light transmitted through the annular lensarea to have an integer multiple of a wavelength of the light emittedfrom the light source, when the second substrate is to be used.
 7. Arecording and/or reproducing apparatus device in an optical device andcompatible with disks having different thicknesses, the recording and/orreproducing apparatus comprising: an optical pickup device comprising alight source, an objective lens, facing one of the disks which is placedin the optical device, having a light passing region divided into inner,annular lens and outer regions respectively corresponding to a near axisarea, an intermediate axis area and a far axis area of incident light,wherein curvatures of the central and periphery regions are optimizedfor the one disk if the one disk has a first thickness and a curvatureof the annular region is optimized for the one disk if the one disk hasa second thickness greater than the first thickness, a photo detectorfor detecting light reflected from the one disk, and a separation unitto separate the incident light transmitted from said light source fromthe reflected light reflected by the one disk; and a processing unit toprocess an information signal to control the incident light generated bysaid light source to process the detected light from said lightdetector, wherein a surface of the annular lens area forms a stepdifference with a surface of one of the inner and outer areas, whereinthe surface of the annular lens area forms the step difference with thesurface of the outer area, wherein the step difference is a value suchthat a light path difference between the light passing through the innerarea and the light passing through the annular lens area is an integermultiple of a wavelength of the light emitted from the light source. 8.A recording and/or reproducing apparatus device in an optical device andcompatible with disks having different thicknesses, the recording and/orreproducing apparatus comprising: an optical pickup device comprising alight source, an objective lens, facing one of the disks which is placedin the optical device, having a light passing region divided into inner,annular lens and outer regions respectively corresponding to a near axisarea, an intermediate axis area and a far axis area of incident light,wherein curvatures of the central and periphery regions are optimizedfor the one disk if the one disk has a first thickness and a curvatureof the annular region is optimized for the one disk if the one disk hasa second thickness greater than the first thickness, a photo detectorfor detecting light reflected from the one disk, and a separation unitto separate the incident light transmitted from said light source fromthe reflected light reflected by the one disk; and a processing unit toprocess an information signal to control the incident light generated bysaid light source to process the detected light from said lightdetector, further comprising: a unit on which the light source and thephoto detector are formed adjacent to each other; the separation unitbeing a holographic beam splitter; and a collimating lens to collimatethe light passing through the holographic beam splitter from the lightsource and to transmit the reflected light from the one disk toward theholographic beam splitter; wherein the holographic beam splitter directsthe reflected light toward the photo detector.
 9. The recording and/orreproducing apparatus as claimed in claim 8, further comprising aquarter wave plate disposed between the holographic beam splitter andthe collimating lens.
 10. The recording and/or reproducing apparatus asclaimed in claim 8, wherein the holographic beam splitter is apolarizing hologram.
 11. A recording and/or reproducing apparatus devicein an optical device and compatible with disks having differentthicknesses, the recording and/or reproducing apparatus comprising: anoptical pickup device comprising a light source, an objective lens,facing one of the disks which is placed in the optical device, having alight passing region divided into inner, annular lens and outer regionsrespectively corresponding to a near axis area, an intermediate axisarea and a far axis area of incident light, wherein curvatures of thecentral and periphery regions are optimized for the one disk if the onedisk has a first thickness and a curvature of the annular region isoptimized for the one disk if the one disk has a second thicknessgreater than the first thickness, a photo detector for detecting lightreflected from the one disk, and a separation unit to separate theincident light transmitted from said light source from the reflectedlight reflected by the one disk; and a processing unit to process aninformation signal to control the incident light generated by said lightsource to process the detected light from said light detector, wherein asurface of the annular lens area forms a step difference with a surfaceof one of the inner and outer areas, further comprising: a unit on whichthe light source and the photo detector are formed adjacent to eachother; the separation unit being a holographic beam splitter; and acollimating lens to collimate the light passing through the holographicbeam splitter from the light source and to transmit the reflected lightfrom the one disk toward the holographic beam splitter; wherein theholographic beam splitter directs the reflected light toward the photodetector.
 12. A recording and/or reproducing apparatus which readsinformation from an optical recording medium, the recording and/orreproducing device comprising: an optical pickup comprising a firstlight source to emit a first light, a second light source to emit asecond light, wherein only one of the first and second light sourcesemits the first and second lights, respectively, at a given time, anobjective lens to receive the one of the first and second lights emittedfrom the corresponding one of the first and second light sources, and tofocus the one of the first and second lights emitted toward the opticalrecording medium and pass light reflected from the optical recordingmedium, and a photo detector to receive the light reflected from theoptical recording medium and passed through the objective lens, toreproduce the information; and a processing unit to process informationsignals to control the first and second lights emitted from said firstand second light sources, and to process the received light from saidphoto detector, for the reproduction of the information.
 13. Therecording and/or reproducing apparatus device as claimed in claim 12,wherein the first light source emits the first light if the opticalrecording medium has a first thickness and the second light source emitsthe second light if the optical recording medium has a second thicknessgreater than the first thickness.
 14. The recording and/or reproducingapparatus device as claimed in claim 12, wherein the first light has afirst frequency and the second light has a second frequency differentfrom the first frequency.
 15. The recording and/or reproducing apparatusdevice as claimed in claim 13, wherein the first light has a firstfrequency and the second light has a second frequency different from thefirst frequency.
 16. The recording and/or reproducing apparatus deviceas claimed in claim 12, wherein the objective lens is a single lens. 17.The recording and/or reproducing apparatus device as claimed in claim12, wherein the objective lens includes a light passing region dividedinto inner, annular lens and outer regions, wherein curvatures of thecentral and periphery regions are optimized for the optical recordingmedium if the optical recording medium has a first thickness and acurvature of the annular region is optimized for the optical recordingmedium if the optical recording medium has a second thickness greaterthan the first thickness.
 18. The recording and/or reproducing apparatusdevice as claimed in claim 12, wherein the objective lens includes alight passing region divided into inner, annular lens and outer regions,wherein curvatures of the central and periphery regions are optimizedfor the optical recording medium if the optical recording medium has thefirst thickness and a curvature of the annular region is optimized forthe optical recording medium if the optical recording medium has thesecond thickness.
 19. The recording and/or reproducing apparatus asclaimed in claim 17, wherein a surface of the annular lens area forms astep difference with a surface of one of the inner and outer areas. 20.The recording and/or reproducing apparatus as claimed in claim 18,wherein a surface of the annular lens area forms a step difference witha surface of one of the inner and outer areas.
 21. The recording and/orreproducing apparatus as claimed in claim 12, further comprising: afirst beam splitter to transmit the first light from the first lightsource and to reflect the second light from the second light source; asecond beam splitter to transmit the first light transmitted through thefirst beam splitter and the second light reflected by the first beamsplitter; and a collimating lens to collimate the first light andreflected second light transmitted through the second beam splitter, andtransmit the collimated light to the objective lens; wherein the secondbeam splitter reflects the first and second lights reflected from theoptical recording medium.
 22. The recording and/or reproducing apparatusas claimed in claim 19, further comprising: a first beam splitter totransmit the first light from the first light source and to reflect thesecond light from the second light source; a second beam splitter totransmit the first light transmitted through the first beam splitter andthe second light reflected by the first beam splitter; and a collimatinglens to collimate the first light and reflected second light transmittedthrough the second beam splitter, and transmit the collimated light tothe objective lens; wherein the second beam splitter reflects the firstand second lights reflected from the optical recording medium.
 23. Therecording and/or reproducing apparatus as claimed in claim 12, furthercomprising: a first beam splitter to reflect the first light from thefirst light source; a second beam splitter to transmit the first lightreflected by the first beam splitter and reflect the second lightreflected by the first beam splitter; and a collimating lens tocollimate the first light and reflected second light transmitted throughthe second beam splitter, and transmit the collimated light toward theobjective lens; wherein the first and second beam splitters transmit thefirst and second lights reflected from the optical recording medium tothe photo detector.
 24. The recording and/or reproducing apparatus asclaimed in claim 19, further comprising: a first beam splitter toreflect the first light from the first light source; a second beamsplitter to transmit the first light reflected by the first beamsplitter and reflect the second light reflected by the first beamsplitter; and a collimating lens to collimate the first light andreflected second light transmitted through the second beam splitter, andtransmit the collimated light toward the objective lens; wherein thefirst and second beam splitters transmit the first and second lightsreflected from the optical recording medium.
 25. A recording and/orreproducing apparatus which reads information from an optical recordingmedium, the recording and/or reproducing apparatus comprising: anoptical pickup device comprising a first light source to emit a firstlight, a second light source to emit a second light, wherein only one ofthe first and second light sources emits the first and second lights,respectively, at a given time, an objective lens to receive the one ofthe first and second lights emitted from the corresponding one of thefirst and second light sources, and to focus the one of the first andsecond lights emitted toward the optical recording medium and pass lightreflected from the optical recording medium, a first photo detector toreceive the first light reflected from the optical recording medium andpassed through the objective lens, to reproduce the information, and asecond photo detector to receive the second light reflected from theoptical recording medium and passed through the objective lens, toreproduce the information; and a processing unit to process informationsignals to control the first and second lights emitted from said firstand second light sources, and to process the received first and secondlights from said first and second detectors.
 26. The recording and/orreproducing apparatus device as claimed in claim 25, wherein the firstlight source emits the first light if the optical recording medium has afirst thickness and the second light source emits the second light ifthe optical recording medium has a second thickness greater than thefirst thickness.
 27. The recording and/or reproducing apparatus deviceas claimed in claim 26, wherein the first light has a first frequencyand the second light has a second frequency different from the firstfrequency.
 28. The recording and/or reproducing apparatus device asclaimed in claim 25, wherein the objective lens includes a light passingregion divided into inner, annular lens and outer regions, whereincurvatures of the central and periphery regions are optimized for theoptical recording medium if the optical recording medium has a firstthickness and a curvature of the annular region is optimized for theoptical recording medium if the optical recording medium has a secondthickness greater than the first thickness.
 29. The recording and/orreproducing apparatus as claimed in claim 28, wherein a surface of theannular lens area forms a step difference with a surface of one of theinner and outer areas.
 30. The recording and/or reproducing apparatus asclaimed in claim 19, further comprising: a beam splitter to transmit thefirst light from the first light source and to reflect the second lightfrom the second light source; and a collimating lens to collimate thefirst light transmitted through the beam splitter and the second lightreflected by the second beam splitter, and transmit the collimated lightto the objective lens; wherein the beam splitter transmits the firstlight reflected from the optical recording medium to the first photodetector and reflects the second light reflected from the opticalrecording medium to the second photo detector.
 31. A recording and/orreproducing apparatus compatible with different types of optical memorymedia, the recording and/or reproducing apparatus comprising: anobjective lens having a plurality of portions having different opticalcharacteristics, wherein one of said plurality of lens portions focusessaid light onto one of said optical memory media independent of the typeof said one optical memory medium; wherein said plurality of lensportions include a first portion to focus a light emitted from a lightsource onto said one optical memory medium independent of a thickness ofsaid one optical memory medium, a second portion to focus said lightemitted from the light source onto said one optical memory medium ifsaid optical memory medium has a first predetermined thickness, a thirdportion to focus said light emitted from said light source onto said oneoptical memory medium if said optical memory medium has a secondpredetermined thickness which is different from said first predeterminedthickness, and a surface of the second portion forms a step differencewith a surface of one of the first and third portions; and a processingunit to process an information signal to control the light emitted fromthe light source, and to process the light passed through said objectivelens, wherein the surface of the second portion forms the stepdifference with the surface of the third portion, wherein the stepdifference is a value such that a light path difference between thelight passing through the first portion and the light passing throughthe second portion is an integer multiple of a wavelength of the lightemitted from the light source.